1. Field of the Invention
The present invention relates to an installation for converting hydraulic energy into mechanical or electrical energy, such an installation including a hydraulic turbine designed to have a forced flow of water pass through it coming from an impoundment of water such as a dam reservoir or the like.
2. Brief Description of the Related Art
Under certain conditions, a hydroelectric dam can be a greenhouse gas source. For example, in a tropical environment, decomposition of organic matter that is of plant origin or of geological origin and that is immersed in the impoundment of water can give rise to formation of methane (CH4), of carbon dioxide (CO2), or of other gases. Such a phenomenon takes place, in particular, in impoundments of water bordered with forests or when the impoundment of water was created over a preexisting forest. The methane forms mainly in the zones of the reservoir that are poor in oxygen, i.e. in the vicinities of the bottom and of the stagnant regions along the shore of the reservoir. Carbon dioxide forms mainly at the surface. Methane has a greater greenhouse effect than carbon dioxide.
The gases formed in this way can be discharged into the atmosphere via various routes. They are emitted by diffusion and by bubbling, those phenomena being distributed over the entire surface of the impoundment of water and, in practice, being impossible to avoid. Those gases are thus also emitted at the turbines of the dam insofar as, on passing through the turbine, the water undergoes a large pressure drop. Prior to passing through the turbine, the water is at a high pressure that depends on the depth of the water intake of the feed duct in the impoundment of water, so that a large quantity of each gas can have been dissolved in the water. At the outlet of the turbine, the water is at a relatively low pressure, i.e. at a pressure close to atmospheric pressure, so that the water is less likely to contain dissolved gas. A relatively large quantity of methane and of other gases dissolved in the water can thus be released by bubbling due to the lowering of the pressure of the water resulting from it passing through the turbine(s) of a dam.
In certain installations, such as those known from the article entitled “Mitigation and recovery of methane emissions from tropical hydroelectric dams” by L. Bambace, F. Ramos, I. Lima and R. Rosa, published in Energy (vol. 32, No. 6), it is known that metal boxes can be installed in an impoundment of water in order to prevent the water close to the bottom from entering a feed duct of a turbine. That avoids degassing in the turbine but it does not make it possible to treat the water charged with gas that remains at the bottom of the impoundment. Additional systems independent of the metal boxes, with pumps and spray rotors, must be used in order to degas the water, which consumes energy and is complex to put in place and to operate.